=Paper=
{{Paper
|id=Vol-3262/paper14
|storemode=property
|title=Rule-Based Link Prediction over Event-Related Causal Knowledge in Wikidata
|pdfUrl=https://ceur-ws.org/Vol-3262/paper14.pdf
|volume=Vol-3262
|authors=Sola Shirai,Aamod Khatiwada,Oktie Hassanzadeh,Debarun Bhattacharjya
|dblpUrl=https://dblp.org/rec/conf/semweb/ShiraiKHB22
}}
==Rule-Based Link Prediction over Event-Related Causal Knowledge in Wikidata==
<pdf width="1500px">https://ceur-ws.org/Vol-3262/paper14.pdf</pdf>
<pre>
Rule-Based Link Prediction over Event-Related Causal
Knowledge in Wikidata
Sola Shirai1,2 , Aamod Khatiwada1,3 , Debarun Bhattacharjya1 and Oktie Hassanzadeh1
1
  IBM Research, Yorktown Heights, NY, United States
2
  Rensselaer Polytechnic Institute, Troy, NY, United States
3
  Khoury College of Computer Sciences, Northeastern University, Boston, MA, USA


                                         Abstract
                                         Rich semantic information contained in Wikidata about newsworthy events and their causal relations
                                         may serve as a valuable resource to perform event analysis and forecasting. However, prior work
                                         in leveraging methods such as link prediction over causal event data in knowledge graphs has been
                                         limited. In this work we share our methods and findings to curate a dataset of newsworthy events with
                                         cause-effect relations and apply rule-based link prediction models. We find that the performance of such
                                         models can vary greatly among the various relations contained in our curated data, and we identify
                                         several points of consideration for both the data curation process and model performance when using
                                         knowledge about events that are currently present in Wikidata.

                                         Keywords
                                         Link Prediction, Causal Knowledge, Knowledge Graphs




1. Introduction
Data about past newsworthy events, as well as subsequent events they caused, can serve as a
valuable source of information to reason about ongoing events and make forecasts about the
future. For example, past data about major earthquake events may indicate the occurrence of
consequent events such as a tsunami, economic recessions, or even lynchings.1 The ability to
analyze events and make forecasts using causal relations for such events can be invaluable for
proactive decision making by various organizations.
   One method to represent information about such newsworthy events is to use a knowledge
graph (KG), like Wikidata. Capturing events in this way has the benefit of being unambiguous,
enabling interoperability among different KGs, and providing rich semantic information about
entities and relationships. For some events, Wikidata also includes explicit cause-effect rela-
tionships like has_cause (P828) and has_effect (P1542) – such causal relations can exist


Wikidata’22: Wikidata workshop at ISWC 2022
$ shiras2@rpi.edu (S. Shirai); khatiwada.a@northeastern.edu (A. Khatiwada); debarunb@us.ibm.com
(D. Bhattacharjya); hassanzadeh@us.ibm.com (O. Hassanzadeh)
 0000-0001-6913-3598 (S. Shirai); 0000-0001-5720-1207 (A. Khatiwada); 0000-0002-9125-1336 (D. Bhattacharjya);
0000-0001-5307-9857 (O. Hassanzadeh)
                                       © 2022 Copyright for this paper by its authors. Use permitted under Creative Commons License Attribution 4.0 International (CC BY 4.0).
    CEUR

          CEUR Workshop Proceedings (CEUR-WS.org)
    Workshop
    Proceedings
                  http://ceur-ws.org
                  ISSN 1613-0073




                  1
     E.g., the Kantō Massacre, caused by civil unrest and misinformation in the wake of the 1923 Great Kantō
earthquake
Figure 1: An example of a major earthquake event and its consequent event within Wikidata.


between both specific instances of events and general classes of events (e.g., (earthquake,
has_effect, landslide)). An example of such an event in Wikidata can be seen in Figure 1.
   While Wikidata contains many causal relations, it is still far from complete. To address this,
prior work has applied knowledge extraction methods over text documents to enrich Wikidata
with causal relations expressed in Wikipedia articles [1]. An alternative approach is to utilize
link prediction methods. To predict the effect of an earthquake event, for example, we can
try to predict the tail entity of a link as (earthquake, has_effect, ?t). While a large variety
of link prediction models have been developed in recent years [2], in this work we investigate
the use of rule-based models. Besides including inherent interpretability due to their use of
semantic relations rather than latent features, rule-based models also are capable of performing
inductive link prediction (i.e., link prediction for entities that were unseen during training).
These two factors are especially valuable for event analysis and forecasting, allowing event
forecasts to be performed for entirely new events while providing a level of explainability to
decision makers.
   Despite the potential of leveraging KGs to represent and forecast causal relations among
events, the use of KG-completion and link prediction methods for event forecasting has been
limited [3]. Link prediction literature, on the other hand, has tended to focus on improving
state-of-the-art performance over common experimental datasets rather than applying it to
KGs with causal relations among events.
   In this paper, we aim to bridge this gap by investigating the performance of rule-based link
prediction methods in a KG of causal events extracted from Wikidata. We begin by describing
our data curation methods. Next, we apply two rule-based link prediction models to our dataset
to study their performance. Lastly, we provide an analysis of the results obtained by these
models to identify factors that affect their performance as well as characteristics of event-related
data that is currently captured in Wikidata.
2. Related Work
The task of link prediction in KGs has garnered significant interest in recent years, with a number
of surveys [2, 4, 5] presenting the breadth and variety of models that have been developed. Most
commonly, this task is performed using machine learning models which aim to learn some
latent embedding for the entities and relationships present in the KG. One of the shortcomings
of many such models is that they can only perform link prediction in the transductive setting
– i.e., the model can only learn embeddings for entities that are present in the training data.
Additionally, it remains questionable whether such models are able to appropriately capture the
underlying semantic information [6]. On the other hand, rule-based methods for link prediction
are naturally able to handle inductive link prediction, as they learn symbolic rules based on
entities and their relations. While relatively less attention has been given to rule-based link
prediction models, recent analyses have demonstrated that such models can exhibit state-of-the-
art performance while requiring significantly less training time than many embedding-based
models [7].
   For existing link prediction work, most analysis and experiments for link prediction have
been conducted on standard benchmarks such as FB15k-237 [8] and WN18RR [9]. While such
datasets may serve as a useful means to compare different models, it is unclear if or how these
models might perform on a KG that captures causal relations and events.
   Rule-based link prediction models aim to learn Horn rules which imply a target relation.
Such methods, including AMIE [10], AMIE+ [11], AMIE3 [12], DRUM [13], RUDIK [14], and
RuleN [15], learn rules and compute a confidence for each rule based on factors such as the
number of correct groundings in the background knowledge or the coverage of those rules.
The most notable rule-based link prediction model from recent years is AnyBURL [16], which
learns rules efficiently using a bottom-up strategy. In addition to continued development to the
AnyBURL model by its authors, further work has also been conducted which aims to apply the
learned rules more effectively [17].
   An alternative approach to learning rules is to utilize case-based reasoning (CBR). The key
motivation for CBR approaches [18, 19] is to make predictions for a specific type of relation
by identifying alternative paths through the KG. These alternative paths function equivalently
to how “rules” are viewed in the aforementioned methods. Such alternative paths are chosen
based on searching for similar entities in the KG. A key difference between the CBR models and
rule learning models is that CBR does not require any prior training or learning step (although
for practical considerations, the implementation of such methods precompute and store various
metrics). These CBR approaches have also been extended to performing question answering
over KGs using natural language [20].


3. Event Data Collection
3.1. Causal Event Selection
To curate our dataset of newsworthy events and their causal relations from Wikidata, we first
must decide what events are “newsworthy” and what constitute “causal relations” that we wish
to query. For an example of what we might consider a newsworthy event, consider Wikidata’s
entry for the 1923 Great Kantō earthquake (Q274498). While we can observe that such an event
is an instance of the earthquake class, there is no distinguishing property or class type2 that
can provide us with a meaningful method to filter out what classes to consider as our events
of interest. Attempting to simply query for all entities that have a causal relation also is not
a viable option, as Wikidata contains a large amount of non-event related entities with such
relations (such as reports (Q10429085) and motions (Q96739634) in the Swedish legislature,
which include thousands of causal relations). Therefore, we chose to select a set of classes
of interest by querying Wikidata for all entities that have a link to Wikinews as a means of
identifying events that have received news coverage. Despite the fact that many newsworthy
events do not have Wikinews coverage and/or links, the existing Wikinews links help us identify
the majority of event types (classes) for newsworthy events and their causes and effects.
   From this step, we identified a set of 307 classes as our event classes of interest. Next, we
identified causal relations that we would use to query and collect the initial set of cause-effect
event pairs. From the set of Wikidata properties for causal relations,3 we use the has_cause,
has_immediate_cause, and has_contributing_factor relations, as well as their inverses
(has_effect, immediate_cause_of, and contributing_factor_of, respectively). We
opt to include the inverses of the causal relations because Wikidata only contained triples
for many cause-effect pairs in one direction. For example, the Kantō Massacre (Q16176384)
refers to the 1923 Kantō earthquake as its cause, but the earthquake’s entry does not contain a
has_effect relation to the massacre event. Further details about how these relations are used
in Wikidata to model causes can be found at wikidata.org/wiki/Help:Modeling_causes.
   Our final query thus searched for all entities that are an instance of one of our event classes
of interest and connected to another event of interest by one of our 6 causal relations. This
query resulted in a total of 1,953 causal event pairs spanning 157 unique event types. We
note that causal relations can be one-to-one, one-to-many, or many-to-many, and events may
simultaneously have has_effect and has_cause relations. Our 1,953 event pairs were made
up of 538 unique event entities in total, with 284 unique cause events and 311 unique effect
events.

3.2. Data Curation
Having selected our newsworthy events with cause-effect relations, our second step was to
collect additional relevant triples from Wikidata. Starting from our 538 unique event entities, we
collected triples up to a distance of 3-hops away from each entity. The decision to only collect
up to the 3-hop neighborhood is to keep in line with how most experiments for rule-based
link prediction methods, which follow paths through the KG, tend to limit themselves to only
search up to 3-hops. Additionally, to keep our dataset at a manageable size and quality, we only
collect the 3-hop neighborhood that can be reached by outgoing relations. Several classes that
were reachable from our events had an extremely large amount of incoming triples (notably the
human (Q5) class, which had over 4 million incoming instance_of relations, and the taxon
(Q16521) class, with nearly 3.5 million instance_of relations).

   2
       We interchangably refer to the instance_of (P31) relation in Wikidata as the “type” or “class” of the event.
   3
       https://www.wikidata.org/wiki/Wikidata:List_of_properties/causality
  Lastly, we removed literals (numeric values, date-times, and strings) from the KG. Our final
dataset consisted of roughly 1,080,000 triples, encapsulating 444,228 unique entities and 1,263
unique relations. Due to the manner in which we collected an outgoing 3-hop neighborhood
around events, we also found that a significant number of entities in our dataset contained very
few triples – roughly 70% of the entities only had one triple in the KG. While this would be
problematic if we simply perform link prediction evaluation over all entities, our focus is on
the events with causal relations, all of which have their 3-hop neighborhood of connections
available in our dataset.
  Most Common Cause Event Types        Count      Most Common Effect Event Types           Count
         Disease Outbreak               264                Disease Outbreak                 237
               Disease                  96                      Disease                     206
         Infectious Disease             44        Closing of Educational Institutions       146
            Rare Disease                34                 Social Distancing                112
              Shooting                  32      Declaration of Public Health Emergency      111
                War                     32                Infectious Disease                 93
         Biological Process             31                 Travel Restriction                77
              Conflict                  26                   Clinical Sign                   76
            Phenomenon                  25                 Aviation Accident                 62
             Homicide                   24                     Lockdown                      57
Table 1
The top 10 most common cause and effect event types in our dataset.


   Some of the most common types of cause and effect events in our dataset can be seen in
Table 1. A large number of events related to diseases are included, which we can likely attribute
to entries related to the Covid-19 pandemic. Many similar Covid-related events have highly
similar entries made for each country, resulting in the majority of our most common effect
types also being Covid-related. On the other hand, the most common causes include some more
variety, such as the “war” and “shooting” types.


4. Experiments
4.1. Link Prediction Models
To investigate the performance of rule-based link prediction methods, we apply two models
from recent years – CBR [18] and AnyBURL [16]. CBR performs link prediction for a triple
(ℎ, 𝑟𝑞 , ?𝑡) by first searching for 𝑘 similar entities in the KG. For each similar entity ℎ𝑠 , CBR
samples the KG for 𝑚 alternative paths up to 𝑛 hops in length that can be used to reach the
target entity for the relation 𝑟𝑞 – i.e., for a triple (ℎ𝑠 , 𝑟𝑞 , 𝑡𝑠 ) in the KG, a path of relations
𝑝 = (𝑟1, ..., 𝑟𝑛 ) connecting ℎ𝑠 to 𝑡𝑠 is identified, where 𝑝 ̸= (𝑟𝑞 ). These sampled paths are then
applied to the query triple, following each path 𝑝 starting from the query entity ℎ to reach
candidate tail entities. Candidates are scored based on how many such sampled paths reach
them. The CBR method is very simple, but demonstrated comparable performance to common
KG embedding models in the original publication while requiring no training step.
   On the other hand, AnyBURL performs efficient rule mining using a bottom-up approach.
AnyBURL first learns “bottom rules,” which are Horn rules whose variables are grounded to
specified instances in the KG. The bottom rules are then iteratively generalized, and confidence
scores for each generalization are computed based on the number of body groundings in the
KG that make the rule true. AnyBURL is trained for a set amount of time (up to 1,000 seconds
by default) and has shown competitive performance to state-of-the-art link prediction models
on standard benchmarks4 .

4.2. Experiments
We analyze the performance of CBR and AnyBURL by following standard evaluation procedures
for link prediction tasks in KGs. Our dataset is split into training, validation, and test sets
containing 70%, 15%, and 15% of the overall data, respectively. We run CBR over the training set
using hyperparameter choices to select 5 similar cases and sample 20 paths (similar numbers to
those used in the original publication), and we run AnyBURL using default configurations up to
1,000 seconds. Performance is measured over the test set using Hits@K for K=1 and 10 as well
as Mean Reciprocal Rank (MRR).
   Additionally, we perform experiments to assess the performance of the two link prediction
models as the amount of training data decreases. One benefit of rule-based methods is that they
can often learn rules from a small number of samples, whereas embedding-based models tend
to require a large amount of training data and time to learn useful embeddings. To test this, we
repeat the above experiment while reducing the training dataset size to 90%, 80%, 60%, and 40%
of the original, evaluating against the test set for each size decrease.


5. Results and Discussion
5.1. General Model Performance

                    All Test Triples                            Event-Related Test Triples
   Model         Train % H@1 H@10             MRR         Model   Train % H@1 H@10                 MRR
                  100%      0.126 0.216       0.158                100%     0.139 0.202            0.161
                   90%      0.114 0.198       0.143                 90%     0.127 0.187            0.148
    CBR            80%      0.102 0.180       0.129       CBR       80%     0.114 0.169            0.134
                   60%      0.081 0.142       0.102                 60%     0.081 0.122            0.095
                   40%      0.055 0.095       0.069                 40%     0.055 0.082            0.065
                  100%      0.243 0.362       0.280                100%     0.214 0.329            0.249
                   90%      0.230 0.347       0.267                 90%     0.201 0.311            0.234
 AnyBURL           80%      0.216 0.330       0.251     AnyBURL     80%     0.181 0.287            0.214
                   60%      0.186 0.294       0.219                 60%     0.146 0.245            0.176
                   40%      0.150 0.234       0.180                 40%     0.115 0.199            0.141
Table 2
Model performance comparisons for the Hits@K (H@K) and MRR performance metrics.



   4
       The most recent version of AnyBURL can be accessed at https://web.informatik.uni-mannheim.de/AnyBURL/
   Table 2 displays the performance of the CBR and AnyBURL models over our dataset. For
each model, the performance is compared with decreasing training data size (indicated as the
Train % column). Additionally, we compare the performance of the models over all triples in the
test set (shown on the left of the table) versus the performance when considering only triples
whose head or tail entity are one of our events of interest (on the right).
   In general we can observe that AnyBURL shows superior performance to the simple CBR
model – this is an expected result, considering the previously reported performance metrics.
However, when we specifically focus on triples in the test set related to events, we can observe
that the performance of AnyBURL generally decreases while CBR very slightly increases. This
result is interesting, as we would expect that event-related entities have more complete training
data avaiable due to our data curation methods.

5.2. Performance for Relations of Interest
Table 3 shows a breakdown of the two models’ performance in terms of MRR for the most
common relation types in the test dataset. Test Count refers to the number of triples in the test
dataset for each relation type, while Training Count refers to the number of triples for each
relation that were present in the training set. Note that these counts and performance metrics
are only considering the event-related test triples.

 Most Common Relations               Test Count   Training Count    AnyBURL MRR      CBR MRR
 subclass of (P279)                        1239            26,574           0.125        0.105
 instance of (P31)                          961            59,420           0.458        0.229
 has part(s) (P527)                         354            15,178           0.179        0.283
 has cause (P828)                           318             1,797           0.258        0.296
 drug used for treatment (P2176)            247             3,687           0.602        0.372
 has effect (P1542)                         237             1,369           0.282        0.384
 described by source (P1343)                232            18,862           0.398        0.075
 part of (P361)                             222             9,930           0.422        0.356
 medical condition treated (P2175)          210             3,604           0.741        0.481
 topic’s main category (P910)               207            22,243           0.304        0.773
Table 3
Model performance on the top 10 most common relations for event-related triples.

   We are able to observe some large differences in performance between the two models
for specific relations. For example, while CBR’s performance is incredibly poor compared to
AnyBURL for the described_by_source relation, it performs significantly better for the
topic’s_main_category relation. Of particular interest is their respective performance on
the causal relations between events, where we see slightly better performance by CBR on both
the has_effect and has_cause relations.
   One of the reasons for this discrepancy in performance may be due to how CBR relies on
effectively finding similar entities in the KG to base its predictions on. As our data curation
method revolved around events with causal relations, it is reasonable to assume that adequate
data has been collected on such entities to identify good “similar” entities for the case of the
has_effect relation. On the other hand, many other relations for which CBR performed
poorly were most likely unable to find good matches, or there were insufficient alternatively
paths through the KG to make good predictions. This especially is the case for any nodes that
are on the outer edge of the 3-hop neighborhood which was used to collect our event dataset.
   These results lead to an important consideration, both for data curation, and for performance
analysis on data from Wikidata. When methods for link prediction rely on training data, it is
necessary to consider how the methods used for data curation might lead to an imbalance of
available data or completeness of data surrounding each entity. Additionally, when comparing
performance between models, it is important to understand exactly how the different models
perform better than each other. From our results, while AnyBURL shows superior performance
for link prediction in general, analysis of performance for each relation would suggest that CBR
is in fact superior for causal link prediction.

5.2.1. Performance of Inverse Relations
Among the best performing relations from Table 3, several pairs of inverse relations can be
found (such as has_cause and has_effect, has_part(s) and part_of, and P2176 and
P2175). The inclusion of inverse relations have been criticized as a source of indirect data
leakage in analyses of link prediction methods [21], suggesting that the presence of inverse
relations artificially inflates the performance of link prediction models while limiting their
usefulness in practical applications. For the task of event forecasting, this is an important
point to consider because new events that we are trying to forecast will not have such inverse
relations present in the KG.
   To test this, we filter out inverse relations from the training data and re-run the AnyBURL
model. We focus on assessing the performance for just the has_effect relation in two
experiments – first, removing all inverse relations between entities present in has_effect
triples in the test set, and second, removing all inverse relations among all entities in the training
set (removing any inverse of a triple contained in the test set, and otherwise selecting which
inverse to remove at random) to compare general performance.
   We find that when removing inverse connections in the training triples, the performance
of AnyBURL significantly decreases for this relation. When removing inverses of just the
has_effect relation, AnyBURL’s MRR for predicting has_effect links decreases from 0.282
in the original results to 0.072. When removing all inverses from the training data, the MRR
further decreases to 0.057.
   For the general training set, the MRR and Hits@10 decrease to 0.153 and 0.242, respectively,
when all inverse relations are removed. This indicates that AnyBURL was able to effectively
make use of the inverse relations contained in our dataset – further, it also indicates that our
methods for data curation lead to a large number of inverse relations being included. We
also extend the training of AnyBURL up to 10,000 seconds to observe if better performance
can be achieved. With the 10-fold increase in training time, the model showed very small
improvements, with the MRR increasing to 0.161 and Hits@10 to 0.252.
5.2.2. Patterns in Performance
In general, the performance of these rule-based models shows large variance between different
relation types. Some factors that we believed might be influencing this performance were (1)
the variety of entities connected by certain relations, and (2) the number of paths connecting
entities in relations. Regarding the variety of entities, we mean this to indicate how many
different tail entities a particular relation leads to – for example, the continent relation would
only have 7 tail entities it leads to, while the country relation can connect to a much larger
number of entities. In a trivial case, if a particular relation only ever leads to one entity, a model
such as AnyBURL could learn a rule that always leads to the same entity. On the other hand,
the number of paths connecting entities may be relevant to consider because the rules learned
by AnyBURL are, essentially, paths through the KG. It might serve to reason that the number
of such paths connecting entities leads to differences in performance – a smaller number of
paths might indicate greater precision in the rules, or a larger number of paths might allow for
a better chance of learning a relevant rule.




Figure 2: AnyBURL’s MRR versus the variety of tail entities reached by event-related relations.


   Figure 2 shows a scatterplot of AnyBURL’s performance, where each point represents the
model’s performance for a single relation. The X-axis captures the variety of tail entities reached
by the relation, where points further to the right have a greater variety of tail entities. We can
see a cluster of relations with very poor performance at the bottom-right corner (i.e., relations
which always lead to different tail entities). We also can observe that even relations with very
little variety can show poor performance, as seen by some points on the bottom-left.
   To consider the second point, Figure 3 shows a plot of AnyBURL’s MRR for relations versus
the number of paths connecting entities in the relations. Here, we limit the relations to only
consider the top 20 best performing relations, where the relations occured at least 10 times
in the test data. For each triple, the number of paths between the head and tail entity in the
training data was counted, and the average such count for each triple of a particular relation is
Figure 3: Top 20 best performing relations versus the number of paths connecting the head and tail
entity in the training data.


shown. Here, we once again see no clear pattern in the performance – while the best performing
relation has a low average number of paths connecting its head and tail entities, the second
best performing relation has a relatively high number of connecting paths.




Figure 4: A comparison of the MRR for individual relation types vs the training data size, where 1.0
refers to the “full” training dataset, 0.9 refers to 90%, and so on.
5.3. Impact of Training Data Size
Lastly, we consider the impact of training data size on individual relations. While we saw an
expected general pattern of decreasing performance for the overall evaluation, at the scope
of individual relations we in fact see some interesting results. Figure 4 plots the performance
of AnyBURL’s prediction for 20 relations (once again selecting the top performing relations
with over 10 triples). While we can see a general trend of increased performance as training
data increases for many relations, for several relations we can see that increasing dataset size
sometimes leads to decreased performance. This could be caused by a number of factors, as our
decreased training data was selected randomly. For example, as AnyBURL relies on learning
and mining rules, it is possible that some of the larger datasets included a triple that lead to an
unreliable rule.


6. Conclusion
In this paper, we investigated utilizing link prediction methods over causal event-related knowl-
edge in Wikidata, as a means of analysis of newsworthy events and event forecasting. In
Wikidata, we found that the availability of event entities with causal relations was quite limited
considering the large scale of the KG. In applying two rule-based link prediction methods –
a case-based reasoning model and AnyBURL – we are able to observe limited success in link
prediction. These models show wide variance in their performance across the various relations
found in our curated dataset, with many trivial relations showing high performance while some
relations could not be predicted at all by the models. We also can observe that increasing the
amount of available data does not necessarily lead to improved performance in some experi-
mental settings. We find that the presence of inverse relations heavily impacts the performance
of the rule-based models, leading to nearly a 75% decrease in performance for relations such
as has_effect. This shows that link prediction methods can provide a reliable solution for
enriching event-related knowledge, but may have limited application in event forecasting.
   Towards realizing the potential of using such data for more sophisticated event forecasting, a
major challenge exists in determining how to collect data with a wider coverage of events as
well as how to appropriately apply and evaluate models. Furthermore, without careful curation
and analysis of test data, typical evaluation metrics that average together the performance over
various relations can lead to models whose performance is inflated by over-performing on a
number of relations. In the future, we plan to experiment with link prediction over Wikidata
knowledge that is enriched through knowledge extraction from Wikipedia articles [1] as well
as performing more thorough explorations into applying various link prediction models to
causal KGs [22]. We hope to develop a robust link prediction framework that can reliably derive
certain kinds of event-related relations, and contribute the outcome to Wikidata in the form of
triples with explanations on how they have been derived.
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